allow loading local pages from local IPs

Summary:
The URL validation regex excluded local IPs. This seems unnecessary
limiting, as it makes it very hard to reach perfectly valid local
webservers (often found it smart homes, for example).

This patch removes this restriction, allowing me to reach some lights,
my NAS and a bunch of other local servers from Angelfish.

Other webbrowsers do not restrict this, and it's unclear to me from
looking at the source why Angelfish should.

Test Plan: Surfed to my local webservers, they now work.

Reviewers: Plasma, schmeisser

Reviewed By: Plasma

Subscribers: bshah

Differential Revision: https://phabricator.kde.org/D26141